1. Field of the Invention
This invention relates to a magnetostatic device utilizing ferromagnetic resonance of YIG(Yttrium-Iron-Garnet) which has frequency-variable characteristics for a wide frequency range and a chip therefor. It comprises a YIG film deposited on a basic plate of GGG(Gadolinium-Gallium-Garnet), on which other components are formed by a photo-lithograpy technology. More specifically, the invention relates to a magnetostatic resonator and a chip therefor which can be incorporated in a relatively small metallic package.
2. Description of the Prior Art
A magnetostatic wave device utilizing ferromagnetic resonance typically is used in a delay line, a filter in a radar system or a communication system for microwave.
FIG. 15(a) and FIG. 15(b) illustrate the structure of a conventional magnetostatic wave resonator described in IEEE Ultrasonic symposium, 1984, pp 164-167. FIG. 15 (b) is a G--G cross-sectional view of the device shown in FIG. 15(a). The magnetostatic wave device includes a chip 6 of YIG 2/GGG 1 having a size of 4 mm.times.1.4 mm and coupling lines 8 on a dielectric substrate 7 located on a ground 5. It resonates at a frequency of about 12 GHz. A bias magnetic field H.sub.0 is applied perpendicular to the surface of YIG film 2 in the chip 6.
One of the coupling lines 8 is an input terminal and the another is an output terminal on the chip 6. When the input terminal is connected to a high frequency power source, a magnetostatic wave occurs in the YIG film 2 and the magnetostatic wave can be detected at the output terminal which is spaced a predetermined distance from the input terminal.
The resonance frequency of the magnetostatic wave depends on the shape of the chip 6 and the bias magnetic field H.sub.0.
A resonance frequency can be obtained by adjusting the bias magnetic field H.sub.0 to pass only a desired frequency of signal to the output terminal from the input terminal.
But the conventional magnetostatic wave device shown in FIG. 15 is inferior in that it is difficult to incorporate in a compact package, primarily because the electrodes 8 used to exite the magnetostatic wave are not arrayed on nor integrated with the chip.
There is also the problem that it is difficult to locate the chip 6 and the electrodes 8 exactly at the desired positions, and it is necessary to take precautions to maintain exactly the width of YIG film 2 of the chip 6 and to polish precisely the end surface of the chip, to establish a high Q-value of resonance in the device.
Murakami et al. disclose another type of ferromagnetic resonator as shown in FIG. 16 in their U.S. Pat. No. 4,547,754. In that resonator, higher frequencies of parasitic modes are reduced by a circular ditch or groove formed in a YIG film or a disk shaped thinner portion formed in the YIG film.
Murakami et al. mention the problem that undesirable modes of magnetostatic resonances are caused by the peripheral area extending inwardly about 1 mm or less from the end of YIG film where a demagnetization field increases drastically up to the end the YIG film, which demagnetization field causes a drastic variation in the inside magnetic field Hi as indicated in FIG. 2 of Murakami et al, even if the YIG film is located in a uniform magnetic field.
Each mode of resonances is described as (n, N).sub.m 7, when a magnetic field is applied perpendicular to the surface of a ferrimagnetic material of film, as analized in Journal of Applied Physics, Vol. 48, July 1977, pp. 3001-3007. A (n,N).sub.m mode means a mode having n joints along the peripheral direction, N joints along a diameter direction and (m-1) joints along the thickness direction of the YIG film.
For example, the (1,1).sub.1 mode is the main mode of magnetostatic resonances, if a wholly uniform magnetic field exists in the YIG film.
When the main mode identified as (1,1) is utilized in, for example, a bandpass filter or other devices, other modes are parasitic modes of higher harmonic frequencies in the device.
Although Murakami et al. present improvements to suppress undesirable modes of resonances, they are inferior in the following points.
It is difficult to remove accurately only a partial thickness of a very thin YIG film by a chemical etching process, and the steps used in the etching process on the YIG film surface damages transducers which are directly formed on the chip.
The object of the present invention is to provide a compact shaped magnetostatic wave device including a YIG/GGG chip having precise dimensions which is incorporated with transducers located precisely at desired positions to further suppress undesired higher harmonic frequencies of subsidiary or parasitic waves.